This proposal requests support for a Keystone Symposia meeting entitled Hematopoiesis, organized by David Traver, Amy J. Wagers and Emmanuelle Passegui, which will be held in Big Sky, Montana from March 27 - April 1, 2011. As a paradigmatic model of developmental and regenerative biology, studies of the hematopoietic system have been critical in establishing fundamental principles in growth factor signaling, transcriptional regulation, organ patterning and stem cell biology. Now, with new and emerging knowledge, we are beginning to develop a true molecular understanding of the mechanisms by which blood cells are created and maintained, and how their function may be perturbed in the context of hematopoietic deficiency and malignancy. In addition, sophisticated embryological studies have finally documented the existence of bipotential hemogenic endothelium in developing organisms, and striking technological advances in in vivo imaging and cell identification strategies have provided our first direct visualization of blood cell formation in situ. All of this has indicated the key importance of cell migration and interaction with discrete niches in the direction of cell fate and function. Finally, when turned to the study of blood diseases, these tools have provided unexpected insights into the microenvironmental controls that regulate hematopoietic (dys)function during aging and malignancy. In light of these exciting developments, it is clear that the time has come to again bring together hematopoiesis researchers to facilitate and accelerate the exchange of new knowledge and ideas. This meeting will include a diverse group of scientists studying hematopoiesis with new technologies and complementary model systems. Speakers have been invited from all career stages, and talks will focus on current findings, emerging opportunities, and immediate challenges within the field. We expect this meeting to serve as a catalyst to develop new ideas and collaborations, and to enhance and encourage the creative and interactive science that will continue to push forward discoveries in this important area of research.